1. Field of the Invention
The present invention relates to a device for forming the shed of a weaving loom.
2. History of the Art
It is known that, in order to open the shed of the layer of warp yarns of a weaving loom, a mechanism is used which is adapted to lift a certain number of these yarns while leaving the others at their lower level so as to allow the passage of a pick.
Shed forming devices are generally composed of hooks coupled to a heddle and which are lifted and lowered by griffe boxes, a selection being made from a card to determine whether or not the hooks are gripped by the griffe boxes.
Systems also exist wherein each harness cord is associated with the first pulley of a lifting beam which comprises a second pulley surrounded by a funicular member of which the ends are fast secured with two hooks which are continually displaced vertically in reciprocal manner in opposite directions by means of appropriate devices such as knives. When it is desired to lift a harness cord, one of the mobile hooks is gripped when, at its top dead centre, by a retaining hook generally actuated by an electro-magnet. Such a device is described in German Patent Application No. 2 204 815 withdrawn since June 1974. The different elements of the shed forming devices of the type described in that Patent Application are free in space, this leading to a large number of drawbacks. The mobile hooks associated with the ends of the funicular element are firstly in the isolated state, with the result that, if a harness cord breaks, it is very difficult to replace, all the more so as it is remote from the edge of the device in question.
It is also observed that the lifting beam, i.e. the system with two pulleys of which one is partially surrounded by the funicular element ensuring connection between the two mobile hooks, while the other cooperates with the harness cord, is subjected to parasitic movements. A pendulum movement is very often observed of the lifting beam, as well as its tendency to rotate. These different drawbacks have led to a limitation of the number of harness cords used on the known high-speed machines.
There again, a break of the funicular element brings about a drop of the lifting beam and its harness cord.